Distance relaying



Feb. 7, 1967 W. K. SONNEMANN DISTANCE RELAYING Filed June 7, 1963 AMPLIFIER DIRECTIONAL 9 RELAY INVENTOR William K. Sonnemann IZQZZMQ ATTORNEY United States Fatent Gfifice 3,303,390 DISTANCE RELAYING Wiliiam K. Sonnemann, Roselle Park, N.J., assignor to Westinghouse Electric Corporation, lEast Pittsburgh, Pa., a corporation of Pennsylvania Filed June 7, 1963, Ser. No. 286,390 Claims. (Cl. 311-36) My present invention relates to relays for protection of alternating current circuits, and particularly to the provision of improved impedance or distance relay arrangements.

In the relaying art it is conventional practice to plot the operating characteristic of a distance or impedance relay of the step-distance type as a circle on a diagram empl oying Cartesian coordinates. Usually in such a diagram, ordinates represent reactance values and abscissas represent resistance values. With a true impedance relay, the operating characteristic is a circle centered at the origin of the coordinate axes. As applied to a transmission line such as a true impedance is independent of the phase angle of the impedance to which it responds. For this reason the true impedance relay sometimes does not distinguish between a condition representing a line fault to which it should respond and certain maximum load conditions to which it should not respond.

A number of suggestions have been made for providing an impedance relay which discriminates to some degree between fault conditions and maximum load conditions. One suggestion employs a modified impedance relay which has an operating characteristic in the form of at least one circle which is offset so that the center of the circle does not coincide with the origin of the coordinates on which the circle is plotted. Examples of such a relay are described in Papers Nos. 58-26, and 19 on Compensator Distance Relaying which appear in the June 1958 Transactions, Power Apparatus and Systems, of the American Institute of Electrical Engineers, New York City, and in application of Serial No. 80,941, filed January 5, 1961, now Patent No. 3,173,060, by Robert G. Lakin and assigned to the same assignee.

It is also possible to make the relay arrangement insensitive to impedance values differing in phase angle markedly from the phase angle of the transmission line being protected. This may be accomplished by means of one or more auxiliary relays or by providing a relay having a non-circular operating characteristic which is proper- 1y contoured. Preferably, the non-circular operating characteristic takes the form essentially of an ellipse having its major axis lined up with the impedance angle of the transmission line being protected and having a relatively small minor axis.

One object of my invention is to provide an improved arrangement for a distance or impedance relay which is selective in operation to trip a circuit breaker as to the phase angles between the line current and voltage at the point where the relay is located.

Another object of my invention is to provide an improved alternating current impedance relay having an operating characteristic which is approximately elliptical.

Another object of my invention is to provide a relay which will protect a long reach of a transmission line against faults characterized by the line impedance, but be non-responsive to faults of smaller magnitude which present impedances of other phase angles.

Still another object is to provide a relay system effecting the above-mentioned purposes by the use of static circuitcomponents.

Other objects of my invention will become evident to those skilled in the art upon reading the following de- 3,303,390 Patented Feb. 7, 1967 scription, taken in connection with the drawings, in which:

FIG. 1 is a graph representing an operating characteristic of the elliptic type which is characteristic of impedance relays embodying my present invention, plotted with purely resistive impedances along the horizontal axis and reactive impedances along the vertical axis;

FIG. 2 is a vector diagram showing certain relationships of currents and voltages in the circuits of my relay arrangement which is useful in the following explanation;

FIG. 3 is a schematic circuit diagram illustrative of one embodiment of my invention; and

FIG. 4 shows an addition which may be made to the circuits of FIG. 3 with the purpose of varying the operating characteristic produced by the latter.

Referring in detail to FIG. 1, it is recognized that the impedance of any alternating current circuit, as, for example, a section of an alternatingcurrent power transmission line, may be represented by a point on a diagram like FIG. 1, where the resistive impedance is plotted along the horizontal coordinate marked R, and the reactive impedance is plotted along the vertical coordinate marked X. The scalar magnitude of the impedance is then represented by the length of the radius vector connecting that point with the origin F of the coordinates. Any straight line, such as FF, drawn through the origin F is the locus of impedances of varying magnitudes, but all having the same phase angle, i.e. all having the same ratio of resistive to reactive component.

The magnitude of the impedance on any given line is a measure of the distance from the measuring station to the fault. In the very extended power systems now in use there are frequently a number of generating stations at different points, and numerous loads and users scattered all over the system. It is highly desirable that all of these generating sources and users should not be disconnected every time a fault occurs at any point on an extensive system. It is possible to avoid this, if means can be provided to interrupt branches of the system conductors in the nearer vicinity of the fault, while leaving more distant generators and users still connected to the lines and able to function as usual. A distance relay, which trips an adjacent circuit breaker only when the impedance presented at its terminals is so low as to show a short circuit within a predetermined distance of it, is able to accomplish this result, since other relays of the system, which are more distant from the short circuit, do not operate. By drawing a line FF through the origin F of coordinates, and making the angle with the R axis, where r and x are respectively the resistance and reactance per unit length of the line conductors (the angle 5 being the natural impedance angle of the line conductors), a graph representative of the line impedance is obtained); and by marking a point G on this line at a distance from the origin F corresponding to the length of the line section which it is desired to have the relay protect against faults, a critical value of impedance is obtained beyond which the relay should not energize a circuit breaker trip-coil for any line short circuit and Within which.any line short circuit should actuate the relay to trip the breaker it controls. The relay is then set to energize the trip-coil of a circuit breaker for impedance values below the critical impedance. Modern power system networks usually have loads connected to draw current which present to the relay an apparent impedance having a numerical value within the critical line length, frequently called the reach of the relay, but these loads usually have impedances of phase angle different from the line 3 angle. They are, accordingly, represented by points lying off the line FF in FIG. 1 and almost always lying near the R-axis.

In an unmodified impedance-relay, actuated to tripping-position at a definite impedance magnitude, the locus of the tripping-impedance would be to a circle with its center at the point F in FIG. 1. However, such an operating characteristic is often undesirable. When a load is connected to a line-section, an associated impedance relay has presented to it a total impedance equal to that of this load plus the impedance of the line between the load and the relay, and if the load is not far from the relay, this total impedance may be less than the maximum tripping value represented by the relay operating characteristic. Consequently, the circuit breaker controlled by the relay may trip even though the phase angle of this total impedance is smaller than the line angle. For practical reasons it is desirable that a relay be available which operates in response to an impedance having the line phase-angle only when such impedance is below a critical value and which does not operate when it is presented with an impedance of similar magnitude of other phaseangle. In order to achieve this desirable operation it is preferable to provide the relay with an operating characteristic in the form of an ellipse.

It is a principal object of my invention to provide an improved relay having such an elliptical operating characteristic with the major axis lined up with the impedance angle of the transmission line being protected and with a relatively small minor axis.

The curve 9 in FIG. 1 is a schematic representation of an elliptical relay operating characteristic having a foci F and F, F being positioned at the origin of the rectangular coordinates R, representing resistance and X representing reactance. The angle [3 equals tanthe angle of the line impedance. The point G lies on the line FF at an impedance corresponding to the impedance of the section of the transmission line which the relay is to protect.

It is a well-known property of an ellipse that, if lines Z and Z are drawn from any point P on the periphery of the ellipse to the two focal points F and F as shown in FIG. 1, the sum of the distances Z plus Z is equal to the numerical value of the length of the major axis Z of the ellipse. It is possible to show from this that 2 2 -2Z,,2Z cos (0[3) where Z is the distance between the focal points F and F. It is also possible to show that the minor axis of the ellipse is equal to /Z.,, -Z and that its concentricity e equals Z /Z The quantities Z, Z and Z are scalar, not vector, values in these equations. Vector quantities herein will carry a superposed dot, for example Z.

In FIG. 1 the line FP may represent the impedance presented to the relay by a load plus the portion of the transmission line between the relay and this load, and the distance FP, to the scale used for FF shows the maximum impedance along the line FP at which the relay would trip its associated circuit breaker. The vector product 12 of line current I and the impedance represents the voltage of the transmission line at the relay, and 0 would be the phaseangle between that voltage and the line current.

The impedance Z; represented by the point G in FIG. 1 is equal to 4 This makes it possible to calculate 2Z l l e and - 2Z.e Z -eZ 1+6 when the desired reach of the relay and the eccentricity e of the elliptical operating characteristic are selected.

The principles of the invention may be applied to the protection of single-phase and polphase electrical systems. For illustrative purposes, FIG. 3 shows the principles applied to a single-phase electrical transmission line operating at a power frequency such as sixty cycles per second and having line conductors or wires L1 and L2. This line also may be considered to represent one phase of a polyphase electrical transmission line.

The line conductors are divided into a first section LS1 and a second section LS2. These sections are selectively connected at a relay station or point by a circuit breaker CB, which has a trip coil CBT and an auxiliary switch CBI. The switch CBI is closed when the circuit breaker is closed and the switch is open when the circuit breaker is open.

A current transformer CT and a voltage transformer VT provide output current and voltage dependent respectively on line current and voltage at the relay station.

FIG. 3 shows in schematic form an impedance relay having an elliptical operating characteristic, and arranged to respond to faults occurring on the line section LS1 which in FIG. 3 extends to the right away from the circuit breaker CB.

Connected in series with the secondary of the current transformer CT are the primary of a current transformer 11 and the adjustable primary of a compensator 12. This compensator may be similar in construction to the compensator described in the previously-mentioned papers entitled Compensator Distance Relaying. As indicated in the papers, the compensator mutual reactance and an adjustable loading resistor 19 determine the phase relationship between the primary current and the secondary induced voltage.

The secondary of the transformer 11 is connected through a suitable full-wave rectifier to apply across a resistor 17 a direct voltage I Z which is dependent on the scalar value of the line current. In the specific embodiment of FIG. 3, two rectifiers 14 and 15 have their anodes connected respectively to the terminals of the secondary of the transformer 11. The cathodes of the rectifiers are connected to the positive terminal of the resistor 17. The negative terminal of the resistor is connected to a center tap on the secondary of the transformer 11. An adjustable loading resistor 13 is connected across the secondary of the transformer 11. A filter capacitor 16 is connected across the resistor 17.

The outputs of the compensator 12 and the transformer VT are connected in series across the input terminals of a full-wave rectifier 21. The output of the rectifier is connected across a loading resistor 27 and a filter capacitor 26. In this manner, a direct voltage E dependent on the scalar value of the voltage E appears across the resistor 27.

The voltage transformer 18 has a primary connected across the secondary of the transformer VT for energization in dependence on line voltage. The secondary of the transformer 18 through a suitable rectifier applies a direct voltage E across a resistor 25 which is dependent on the line voltage E. In the specific embodiment of FIG. 3, the anodes of two rectifiers 22 and 23 are connected respectively to the terminals of the secondary of the transformer 18. The cathodes of the rectifiers are connected to the positive terminal of the resistor 25. The negative terminal of the resistor is connected to a center tap on the secondary of the transformer 18. A filter capacitor 24 is connected across the resistor 25.

By inspection of FIG. 3, it will be noted that a resultant voltage it: applied across the base and emitter of an NPN transistor 32 through a resistor 29 and a rectifier 31. The

- rectifier is poled to permit current flow therethrough only when the voltage I Z exceeds in value the sum of the voltages E'+E which is in the direction required to turn on the transistor. A rectifier 34 is connected across the emitter and baseof the transistor to pass current around the base-emitter junction when the voltage across this junction is poled to maintain the transistor in turnedofi' condition. This protects the junction against damage due to reverse current flow therethrou-gh.

When the transistor turns on, the voltage across the resistor 17 directs a current through a circuit including the collector and emitter of the transistor and a resistor 33. The resulting voltage drop across the resistor is employed to energize the trip coil CBT through the switch CBI for the purpose of tripping the circuit breaker CB. If desired an amplifier AM may be controlled by this voltage drop for the purpose of increasing the energy available for energizing the trip coil CBT.

The NPN transistor may be replaced by a PNP transistor. The changes required by such a substitution are well-known in the art.

The relay arrangement of FIG. 3 compares the scalar value of IL with the sum of the scaler value of E and the scalar value of E When these compared values are equal, the transistor is turned otf and the relay arrangement is energized in accordance with its balance point or reach. The scalar value of IZ exceeds the sum of the scalar values of E-j-E when the impedance seen by the relay arrangement is less than the balance point impedance and the transistor turns on to trip the circuit breaker.

The sum of the scalar values of E-i-E exceeds the scalar value of IZ when the impedance seen by the relay arrangement is greater than the balance point impedance. Under this condition the transistor remains turned off and the circuit breaker remains closed.

As previously pointed out, the scalar values controlling the condition of the transistor represent an elliptical operating characteristic for the relay arrangement.

It is usual practice to subdivide a transmission line into sections selectively connected to each other at spaced relay stations or points by circuit breakers. At each of the relay stations an associated circuit breaker is controlled by three zone relay arrangements. A first zone may extend from the relay station for say ninety percent of a protected line section. The impedance relay arrangement protecting this zone operates with negligible time delay.

A second zone extends substantially into the following protected line section and the second zone impedance relay arrangement operates with time delay of say 0.25 second.

A third zone extends even further to assure backup protection and the third zone impedance relay arrangement operates with a time delay which may be of the order of 1 to 2 seconds.

Each of the zone relay arrangements may be similar to that shown in FIG. 3. In each case the reach" of the relay (the length of PG in FIG. 1) is adjusted to equal the impedance of the desired length of the transmission line. Suitable time delays would be provided for sec- 0nd and third zone operation.

If a relay arrangement of the exact type shown in FIG. 3 is used, certain faults occuring in the line section behind the relay, i.e. in the direction opposite to the reach FG of FIG. 1 would operate the relay to trip the circuit breaker. To avoid this third quadrant response a directional element may be provided to disable the relay from response. For one example, a conventional directional relay DR may open a disabling contact in the tran sistor input circuit when power flow changes to the nontripping direction. This provision ordinarily would not be requisite for the third zone relay.

The input circuit of the transistor also may be rendered ineffective by opening a switch S. If desired the contacts of the directional relay DR may replace the switch S.

Another expedient involves the ofifset of the ellipse 9 of FIG. 1 so that the point H coincides with the origin of the diagram as represented by the dotted ellipse 9A. An offset of the ellipse may be provided by inserting a current-derived voltage between the transformers VT and 18 as shown in FIG. 4.

Referring to FIG. 4 a current-derived voltage is obtained from a transducer 41 which may be similar in construction to the compensator 12. The primary of the transducer is connected by conductors 41A and 41B in series with the primaries of the transformers 11 and 12; the link 41C between the conductors being removed under these circumstances. The secondary 42 of the transducer is connected in series with the secondary of the transformer VT to provide a resultant voltage for energizing the primary of the transformer 18. The voltage of the secondary of the transducer 41 may be adjusted to provide an olfset of the desired magnitude and direction.

When a fault occurs close to a relay station, the line voltage may drop in magnitude to a value insuflicient to assure proper relay operation. For this reason memory evices are provided in FIGS. 3 and 4 which maintain an adequate voltage magnitude for a time sufiicient to assure the desired relay operation.

The memory device may take the form of a parallel resonant circuit comprising an inductance coil 46 and a capacitor 45 tuned to the line frequency and connected across the primary of the transformer 18 in FIG. 1 or a series resonant circuit connected in series with the primary as shown in FIG. 4. The series resonant circuit is preferred and is tuned to line frequency. As shown in FIG. 4 the series resonant circuit includes a capacitor 45A and an inductance coil 46A. If the parallel coil 46 and capacitor 45 are employed an impedance 47 should be provided to prevent a fault on the line adjacent the relay station from rendering the parallel coil and capacitor ineffective.

In FIG. 3 the magnitude of the resistance of the resistor 13 may be adjusted for the purpose of adjusting the length of the major axis of the ellipse. The phase angle of the compensator may be adjusted for the purpose of adjusting the valve of the angle [3 of FIG. 1. The magnitude of the compensator voltage output is adjustable to control the distance between the focal points F and F of FIG. 1.

Although the invention has been described with refer ence to certain specific embodiments thereof, numerous modifications falling within the spirit and scope of the invention are possible.

I claim as my invention:

1. In a protective relay for an alternating current line, a first means for producing a voltage having a scalar value proportional to the line current, a second means producing a voltage having a scalar value proportional to the line voltage at said relay, and a third means producing a voltage proportional to the scalar value of the vector quantity E-ZJ where E is the vector quantity proportional to line voltage, I a vector quantity proportional to line current, and Z is a vector quantity having a phase angle equal to the phase angle of the natural impedance of that portion of the line which is to be protected, and a signal-output circuit energized Whenever the voltage produced by said first means exceeds the sum of the voltage produced by said second means plus the voltage of said third means.

2. An apparatus for use on an alternating current line comprising a first means for producing a voltage having a scalar value proportional to the line current i, a second means for producing a voltage proportional to the scalar value of the line voltage E, a third means for producing a voltage proportional to the scalar value of a quantity E-iZ where i, E, and Z, are vector quantities, and Z has a phase angle equal to the phase angle of the natural impedance of the portion of the line which is to be protected, and means for balancing the voltage produced by the first said means against the sum of said voltages produced by said second and third means.

3. A protective relay for alternating current lines comprising a first means for rectifying a voltage proportional to the line current to produce a first direct voltage, a second means for rectifying a voltage proportional to the line voltage to produce a second direct voltage, a third means for producing a voltage proportional to the vector quantity EI'Z' where E is a vector proportional to the line voltage, l a vector proportional to the line current, and Z is impedance quantity having a phase angle substantially equal to the line angle of the portion of the line to be protected, means for rectifying the voltage produced by said third means to produce a third direct voltage, and means to actuate said relay whenever said first direct voltage exceeds the sum of said second direct voltage plus said third direct voltage.

4. An apparatus for use on an alternating line comprising a first means for producing a voltage having a scalar value proportional to the line current i, a second means for producing a voltage proportional to the scalar value of the line voltage E, a third means for producing a voltage proportional to the scalar value of the quantity E'I'Z' where i, E and Z are vector quantities, and means for balancing the voltage produced by said first means against the sum of the voltages produced by said second and third means to thereby produce an elliptical impedance characteristic.

5. The arrangement described in claim 2 wherein said first means comprises a transformer having a first primary energized by line current and having a first secondary feeding a first impedance shunted by a rectifier energized in accord with the terminal voltage thereof to send current through said first resistor load, said second means comprises a transformer having a second primary energized in accord with said line voltage and a second secondary feeding a rectifier to send direct current through a second resistor load, and said third means comprises a compensator having a third primary energized by line current and a third secondary, means connecting said third secondary in series with the second secondary, said compensator being effective to provide in its said third secondary a voltage proportional to said Z a third resistor load, a rectifier, means connecting said last-named rectifier between said second secondary and said third resistor load for sending direct current through said third resistor load.

6. Apparatus for protecting a predetermined section of an alternating current line comprising, means connected to said line for energization therefrom, said means having first and second output connections energized with first and second alternating signals which represent in magnitude and phase the voltage and current quantities respectively which are existent at a first end portion of said section, a first network including a first pair of output terminals, means connecting said first network to one of said output connections, said network being effective to energize its said first pair of output terminals with a first output quantity having a characteristic which varies as a function of the magnitude of a characteristic of the signal supplied by one of said output connections, a second network having a circuit means providing a phase shifted signal, means connecting said second network to said one output connection for energization of said circuit means by the sign-a1 supplied by said one connection, said second network having a second pair of output terminals energized from said circuit means with a second alternating output quantity having a phase shifted relation to the signal supplied by said one connection, a third network having third pair of output terminals, means connecting said third network to the other of said output connections, said third network being effective to energize said third output terminals with a third alternating output quantity having a predetermined phase relation with respect to the signal supplied by said other output connection, a first combining circuit having a fourth pair of output terminals, means connecting said first combining circuit to said second and third pairs of output terminals, said first combining circuit being effective to energize said fourth pair of output terminals with a fourth output quantity having a characteristic which varies as a function'of the vector difference of said second and third output quantities, a fourth network having a fifth pair of output terminals, means connecting said fourth network to said other output connections, said fourth network being elfective to energize said fifth pair of terminals with a fifth output quantity having a characteristic which varies as a function of the magnitude of the signal supplied by said other output connection, and a second com-bining network having a sixth pair of output terminals, rneans connecting said second combining network to said first pair of terminals and to said fourth pair of terminals and to said fifth pair of terminals, said second combining network being effective to energize said sixth pair of output terminals with a quantity which represents the difference between said characteristic of said first output quantity and the sum of said characteristic of said fourth and said fifth output quantities.

7. Apparatus for protecting a predetermined section of an alternating current line comprising, means connected to said line for energization therefrom, said means having first and second output connections energized with first and second alternating signals which represent in magnitude and phase the voltage and current quantities respectively which are existent at a first portion of said section, a first network including a first pair of output terminals, means connecting said first network to said second output connection, said first network being effective to energize its said first pair of output terminals with a first o-utput quantity having a characteristic which varies as a function of the magnitude of a characteristic of said second signal, a second network having a circuit means providing a phase shifted signal which is of a magnitude dependent upon the magnitude of the signal supplied thereto, means connecting said second network to said second output connection for energization of said circuit means by said second signal, said second network having a second pair of output terminals energized from said circuit means with a second alternating output quantity having a phase shifted relation to said second s gnal as determined by said circuit means, a third network having third pair of output terminals, means connecting said third network to said first output connection, said third network being effective to energize said third output terminals with a third alternating output quantity having a predetermined phase relation with said first signal, a first combining circuit having a fourth pair of output terminals, means connecting said first combining circuit to said second and third output terminals, said first combining circuit being effective to energize said fourth pair of output terminals with a fourth output quantity having a characteristic which varies as a function of the vector difference of said second and third output quantities, a fourth network having a fifth pair of output terminals, means connecting said fourth network to said first output connection, said fourth network being effective to energize said fifth pair of terminals with a fifth output quantity having a characteristic which varies as a function of a characteristic of said first signal, and a second combining network having a sixth pair of output terminals, means connecting said second combining network to said first pair of terminals and to said fourth pair of terminals and to said fifth pair of terminals, said second combining network being effective to energize said sixth pair of output terminals with a quantity which represents the difference between said characteristic of said first output quantity and the sum of said characteristics of said fourth and said fifth output quantities.

8. In combination a section of an alternating current line, signal deriving apparatus connected to said line and having first and second output connections energized with a voltage and a current signal, said voltage and current signals having a magnitude and a phase diiference representative of the magnitude and phase difference of the voltage and current quantities respectively which are existent at a first portion of said section, said apparatus having a first network including an impedance element, means connecting said first network to said second output connection for energization of said impedance element by said current signal, said first network having a first pair of output terminals, said first network being effective to energize its said first pair of output terminals with a first output potential having a magnitude which varies as a function of the magnitude of said current signal, a second network having a circuit means for establishing a phase shifted voltage signal having a magnitude proportional to the magnitude of the signal supplied thereto, means connecting said second network to said second output connection for energization of said circuit means by said current signal, said second network having a second pair of output terminals energized from said circuit means with a second alternating outputpotential having a phase shifted relation to said current signal as determined by said circuit means, a third network having thirdpair of output terminals, means connecting said third network to said first output connection, said third network being effective to energize said third output terminals with a third alternating output potential having a predetermined phase relation with said voltage signal, a first combining circuit having a fourth pair of output terminals, means connecting said first combining circuit to said second and third output terminals, said first combining circuit being effective to energize said fourth pair of output terminals with a fourth output potential having a magnitude which represents the vector difference of said second and third output potentials, a fourth network having a fifth pair of output terminals, means connecting said fourth network to said potential output connection, said fourth network being effective to energize said fifth pair of terminals with a fifth output potential having a magnitude which varies as the magnitude of said potential signal, and a second combining network having a sixth pair of output terminals, means connecting said second combining network to said first pair of terminals and to said fourth pair of terminals and to said fifth pair of terminals, said second combining network being effective to energize said sixth pair of output terminals with a potential having an output potential which is dependent upon the difference between the magnitude of said first output potential and the total magnitude of said fourth and said fifth output potentials.

9. The combination of claim 8 in which said first portion of said section is at a first end portion of said section, said circuit means has an impedance characteristic representative of the actual impedance of said line section whereby said phase shifted voltage signal is representative of the magnitude and phase of the voltage drop through said line section, said first and fourth networks and said first combining circuit each including rectifying means whereby said first and said fourth and said fifth output potentials are unidirectional in nature.

10. In combination, first and second pairs of signal energized terminals, 21 first pair of control terminals, a first pair of output terminals, a first rectifier, a first impedance, means connecting said impedance element and said rectifier between said first pair of signal terminals and said first pair of output terminals for energization of said first pair of output terminals by a first unidirectional output quantity having a magnitude dependent upon the magnitude of the signal applied to said first pair of signal terminals, a second pair of output terminals, 21 second rectifier, a phase shifting network having input and output connections and effective to energize its said output connection with an output alternating quantity which is phase shifted with respect to an input alternating quantity applied to its said input connection, means connecting said input connection to said first pair of signal terminals, a combining circuit having a third pair of output terminals, means connecting said combining circuit to said output connection and to said second signal terminals, said combining circuit being effective to energize said third pair of output terminals by a second quantity which is the vector difference of the signal at said second signal terminals and said output alternating quantity at said output connection, means connecting said second rectifier and said second impedance element between said third pair of output terminals and said second pair of output terminals for energization of said second pair of output terminals by a third quantity having a magnitude dependent upon the magnitude of said second quantity, a fourth pair of output terminals, a third rectifier, a third impedance element, means connecting said third rectifier and said third impedance element between said second signal terminals and said fourth pair of output terminals for energization of said fourth pair of output terminals by a fourth quantity having a magnitude dependent upon the magnitude of the signal applied to said second pair of signal terminals, a second combining circuit having input and output connections, means connecting said input connections of said second combining circuit to said first and said second and said fourth pairs of output terminals and said output connection of said second combining circuit to said control terminals, said second combining circuit being effective to energize its said output connections with a quantity which represents the difference in magnitude between said first output quantity and the sum of the magnitudes of said third and said fourth quantities.

11. In combination, first and second pairs of signal energized terminals, means energizing said first pair of terminals with an alternating voltage signal and said second pair of terminals with an alternating current signal, a first pair of control terminals, a first pair of output terminals, a first rectifier, a first impedance, a current transformer having primary and secondary windings, means connecting said primary winding between said second pair of signal terminals, means including said first rectifier and said first impedance connecting secondary winding to said first pair of output terminals for energization of said first pair of output terminals by a first unidirectional output potential having a magnitude dependent upon the magnitude of said current signal, a second pair of output terminals, a second rectifier, a compensator having first and second windings and means establishing a voltage in its said second winding which i phase shifted with respect to a current signal applied to its said first winding and of a magnitude determined by the magnitude of the current signal applied to its said first winding, means connecting said first winding of said compensator to said second pair of signal terminals whereby said second winding is effective to supply an alternating output potential which is phase shifted with respect to said alternating current signal applied to said second pair of signal terminals, a combining circuit having two input connections and an output connection means individually connecting said two input connections of said combining circuit to said second winding of said compensator and to said first pair of signal terminals for energization of said output connection by a second alternating potential which is the vector difference of said voltage signal at said first signal terminals and said alternating output potential at said second winding of said compensator, mean connecting said second rectifier between said output connection of said combining circuit and said second pair of output terminals for energization of said second pair of output terminals by a second unidirectional potential having a magnitude dependent uponthemagnitude of said second alternating potential, a third pair of output terminals, a third rectifier, means connecting said third rectifier between said first pair of signal terminals and said third pair of output terminals for energization of said third pair of output terminals by a third unidirectional potential having a magnitude dependent upon the magnitude of the voltage signal applied to said first pair of signal terminals, a second combining circuit having input and output connections, means connecting said input connections of said second combining circuit to said first and said second and said third pairs of output terminals and said output connection of said second combining circuit to said control terminals, said second combining circuit being effective to energize its said output connection with a quantity which represents the difference in magnitude of said first unidirectional potential and the sum of the magnitudes of said second and said third unidirectional potentials.

12. The combination of claim 11 with an electric transmission line having end sections and an intermediate section, said intermediate section having a predetermined magnitude of resistance and inductance per unit length, said first and second pairs of signal energized terminals being connected to one of said end sections of said transmission line by means of potential and current transforming means respectively, said phase shifting means of said compensator establishing substantially the same magnitude of phase shift in said secondary winding of said compensator as is established by said predetermined magnitude of said resistance and inductance of said intermediate line section.

13. In combination, first and second pairs of signal energized input terminals, a first current actuated network including input and output connections and an impedance element anda first rectifier, said network being characterized by the fact that a first unidirectional voltage is established at its aid output connection as a consequence of the passage of current through its said input connection, the magnitude of said first voltage being determined by the magnitude of said impedance element, a second current actuated network having input and output connections and inductive and non-reactive impedances, said second network being characterized by the fact that a first alternating voltage is established at its said output connection as a consequence of the passage of current through its said input connection, said first alternating voltage being of a magnitude and phase with respect to the current flowing through its said input connection as determined by the magnitude of and the ratio of its said inductive and non-reactive impedances, means connecting said input connections of said networks to said first pair of input terminals for passage of current through said input connections of said networks by current quantities the magnitudes of which vary in response to variations in magnitude of the signal current flowing between said first pair of input terminals, a first alternating voltage combining network having first-and second input connections and an output connection, means connecting said first input connection of said first voltage network to said second pair of input terminals and said second input connection of said first voltage network to said output connection of said second current actuated network, said first voltage combining network including a second rectifier and being effective to provide at its said output connection a unidirectional voltage equal to 12 the vector difference of the voltages applied to its said input connections, a second combining network having first and second and third input connections and an output connection, means connecting said first input connection of said second combining network to said output connection of said first current network, means connecting said second input connection of said second combining network to said output connection of said first combining network, means connecting said third input connection of said second combining network to aid second pair of input terminals, said last-named means including a rectifying means, and a polarized control device connected to said output connection of said second combining network. 7

14. The combination with claim 13 of an electrical transmission line having a first end portion and an intermediate portion to be protected connected between said first end portion and a load, first means connecting said first pair of signal terminals to said first end portion for energization thereof with a signal current quantity representative of the current flowing from said first end portion into said intermediate portion, second means connecting said first end portion to said second pair of signal terminals for energization thereof with a signal voltage quantity representative of the voltage present at said first end portion, the magnitude of said impedance element being so related to the magnitude of the current signal supplied thereto that a potential of a first magnitude is developed at said first input connection of said second combining network when current of a predetermined magnitude flows through said intermediate portion of said line, said predetermined magnitude of current being the magnitude of the fault current which flows through said intermediate portion of said line when said fault is substantially at the portion of said line closely adjacent said load, the magnitudes of said inductive and non-reactive impedances being so related to the magnitude of the current signal supplied to said second current network that a potential of a second magnitude is developed at said second input connection of said second combining network when current of said predetermined magnitude flows through said intermediate portion of said line, said intermediate portion of said line having an impedance such that with said predetermined magnitude of current flowing therethrough the potential drop thereacross is of a third magnitude, said third magnitude of potential being equal to the sum of one half said first magnitude of potential plus one half of said second magnitude of potential.

15. In combination, first and second pairs of signal energized input terminals, a tuned network, a first current actuated network including input and output connections and an impedance element, said network being characterized by the fact that a first voltage is established at its said output connection as a consequence of the passage of current through its said input connection, the magnitude of said first voltage being determined by the magnitude of said impedance element, a second current actuated network having input and output connections and inductive and non-reactive impedances, said second network being characterized by the fact that a second voltage is established at its said output connection as a consequence of the passage of current through its said input connection, said second voltage being of a magnitude and phase with respect to the current flowing through its said input connection as determined by the magnitude of and the ratio of its said inductive and non-reactive impedances, means connecting said input connections of said networks to said first pair of input terminals for passage of current through said input connections of said networks by current quantities the magnitudes of which vary in response to variations in magnitude of the signal current flowing between said first pair of input terminals, a first voltage combining network having first and second input connections and an output connection, means connecting said first input connection of said first voltage network to said second pair of input terminals and including said tuned network, means connecting said second input connection of said first voltage network to said output connection of said second current actuated network, said first voltage combining network being effective to provide at its said output connection a voltage equal to the vector difference of the voltages applied to its input connections, first and second and third rectifying means, a second combining network having first and second and third input connections and an output connection, said second combining network being effective to add the potentials applied to its said second and third input connections to provide a sum potential and to supply to its said output connection a potential which is the difference between said sum potential and the potential applied to said first input connection of said second combining network, means connecting said first input connection of said second combining network to said output connection of said first current network and including said first rectifying means, means connecting said second input connection of said second combining network to said output connection of said first combining network and including said second rectifying means, means connecting said third input connection of said sec-0nd combining network to said second pair of input terminal and including said third rectifying means and said tuned network, and a polarized control device connected to said output connection of said second combining network.

References Cited by the Examiner UNITED STATES PATENTS 8/1947 Lenehan 317-36 1/1950 Goldsborough 31736 MILTON O. HIRSHFIELD, Primary Examiner.

" 20 I. D. TRAMMELL, Assistant Examiner. 

1. IN A PROTECTIVE RELAY FOR AN ALTERNATING CURRENT LINE, A FIRST MEANS FOR PRODUCING A VOLTAGE HAVING A SCALAR VALUE PROPORTIONAL TO THE LINE CURRENT, A SECOND MEANS PRODUCING A VOLTAGE HAVING A SCALAR VALUE PROPORTIONAL TO THE LINE VOLTAGE AT SAID RELAY, AND A THIRD MEANS PRODUCING A VOLTAGE PROPORTIONAL TO THE SCALAR VALUE OF THE VECTOR QUANTITY E-ZCI WHERE E IS THE VECTOR QUANTITY PROPORTIONAL TO LINE VOLTAGE, I A VECTOR QUANTITY PROPORTIONAL TO LINE CURRENT, AND ZC IS A VECTOR QUANTITY HAVING A PHASE ANGLE EQUAL TO THE PHASE ANGLE OF THE NATURAL IMPEDANCE OF THAT PORTION OF THE LINE WHICH IS TO BE PROTECTED, AND A SIGNAL-OUTPUT CIRCUIT ENERGIZED WHENEVER THE VOLTAGE PRODUCED BY SAID FIRST MEANS EXCEEDS THE SUM OF THE VOLTAGE PRODUCED BY SAID SECOND MEANS PLUS THE VOLTAGE OF SAID THIRD MEANS. 